Voltammetric measurements showed in the previous paper that charge transfer is accompanied with CO adsorption on Cu electrode. Adsorbed CO is present at Cu electrode surface below the potential of the cathodic charge transfer, and not present above the potential, as confirmed by infrared spectroscopy. This article reports significant features of in situ infrared spectra of adsorbed CO in detail, obtained with a Cu polycrystaf electrode in aqueous electrolytes at 0 to 2ยฐC with regard to electrochemical reduction of CO, to hydrocarbons. Two infrared absorption peaks were assigned to adsorbed CO. A sharp absorption band appeared at ea. 208Ocm-' between -0.8 and -LOV vs. nhe in 0.2 M KHCO, .
Another absorption peak was broad at 204Ocm-' between -0.7 and -0.8V in the same solution. The infrared absorption intensity is closely related with the amount of charge accompanied with CO adsorption. The infrared absorption bands were studied using D,O electrolyte solutions; the results agreed well with those obtained in H,O electrolyte system. Thus the spectra will not be affected by hydrogen. Infrared absorption bands of reduced CO, were measured as well, showing identical spectroscopic features with adsorbed CO. The reduced CO, is present at -1.0 V at Cu electrode and not present at -0.4 V.
The reduced CO, at Cu electrode is thus identified as adsorbed CO.